Problem: $-\dfrac{8}{10} + \dfrac{4}{12} = {?}$
$ = - {\dfrac{8 \times 6}{10 \times 6}} + {\dfrac{4 \times 5}{12 \times 5}} $ $ = - {\dfrac{48}{60}} + {\dfrac{20}{60}} $ $ = - \dfrac{{48} + {20}}{60} $ $ = -\dfrac{28}{60}$